Why did gas hydrates melt at the end of the last ice age?

GEOMAR researchers find links between sedimentation and methane seeps on the seafloor off the coast of Norway

Large amounts of the greenhouse gas methane are locked up as solid gas hydrates in the continental slopes of ocean margins. Their stability depends on low temperatures and high pressure. However, other factors that influence gas hydrate stability are not as well understood. A German-Norwegian research team has found evidence off the coast of Norway that the amount of sediment deposited on the seafloor can play a crucial role. The study has been published today in the international journal Nature Communications.

Methane hydrates, also known as ‘burning ice’, occur at all ocean margins. The compound of gas and water occurs in the seafloor and it is only stable under relatively high pressures and low temperatures. If the pressure is too low or the temperature too high, the hydrates dissociate (break down), the methane is released and the gas can seep from the seafloor into the ocean. Thus, scientists fear that warming of global water temperatures could destabilize gas hydrates on a large scale. At the same time, it has not been fully understood which other factors influence the stability of gas hydrates.

A team of researchers from the GEOMAR Helmholtz Centre for Ocean Research Kiel together with colleagues from Bergen, Oslo and Tromsø (Norway), have now discovered that large-scale sedimentation caused by melting of glaciers in a region off Norway has played a greater role in gas hydrate dissociation than warming ocean waters.

For their study, the team had investigated the history of gas hydrates in the Nyegga area. “This region off middle Norway is quite interesting if you want to study the dynamics of gases and liquids in the seafloor. There are large gas hydrate deposits, and many crater-like structures, so-called ‘pockmarks’, on the seabed. They are generally associated with gas leaks from deeper gas reservoirs, but their exact origin in this area is still unclear.”

Numerous bathymetric maps, sediment cores and seismic surveys already exist in the Nyegga area, which the researchers used as a basis for the new study. “So we knew that in the final period of the recent Ice Age, between 30,000 and 15,000 years ago, large amounts of sediment were deposited in the region in a relatively short period of time,” explains Dr. Karstens. In a computer model, the team used the available data to simulate the evolution of the seabed and the response of the gas hydrates during this period.

Despite the rising sea level and therefore increasing pressure, the simulation showed that towards the end of the ice age large amounts of gas hydrate became unstable and the released gas escaped through the sediment to the seawater. “Gas hydrates are only stable at a certain depth below the actual seafloor. When dozens of meters of new sediment settle on the seafloor, the solid compounds dissociate at the base of the hydrate stability zone, while new hydrates can form at the upper end of the stability zone. However, if the seafloor is already saturated with gas and the process takes place very quickly, the released gases make their way to the seafloor, without forming new hydrates,” says Dr. Karstens.

The numerical simulations of the seafloor also showed that the pockmarks in Nyegga are likely associated with this phenomenon because they are located right in the area of the largest gas hydrate dissociation event at the end of the Ice Age. Samples from the seafloor confirm this assumption. Mussel shells of the species Isorropodon nyeggaensis were found in the pockmarks. The species is known from its symbiosis with bacteria that feed on methane. The researchers were able to date the shells precisely to the time when, according to the model calculations, the largest gas hydrate dissociation event occurred.

“We show that rapid changes in sedimentation can have a pronounced impact on the gas hydrate system and thus the entire carbon cycle”, Dr. Karstens concludes. To date, this aspect has hardly been considered. However, further studies on other ocean margins are needed to obtain a more global picture, emphasizes the Kiel geophysicist.

I would love to look over their models and see if indeed the gas was emitted at the beginning of the current interglacial. Other models I’ve seen indicate the hydrates become much more unstable at the END of an interglacial, when sea level drops.

“Doesn’t this seem to be contradictory given that between 30,000 and 15,000 years ago the Earth was still in the coldest part of the glacial period?”

No, because the sediment was deposited by the glaciation. Vast quantities of sediments from clay to huge boulders are transported by glacial ice and deposited in the sea in front of the calving ice-front. Heard of the Norwegian fjords? The rock that filled those fjords once is now all on the sea-bottom in front of them.

The only problem you have with your above “response” is that it DID NOT address what I was CRITICIZING you for stating in response to Tom in Florida’s comment wherein you stated: …… “No, because the sediment was deposited by the glaciation.”

Tty, …… “getta clue”. ….. it is scientifically factual and correct that “advancing” glaciers, due to the force of gravity, will erode away the rocks and dirt overlay ….. and carry or push said eroded material “downgrade”, either in front of or within the glacier ice as the de-glaciation process occurs.

“DUH” there is no “glaciation” occurring at the “near-sea level altitude” edge of advancing glacial ice. To state otherwise ….. you would be contradicting yourself, to wit:

“Vast quantities of sediments from clay to huge boulders are transported by glacial ice and deposited in the sea in front of the calving ice-front.”

I shur hope that you are not going to claim that “calving” is a function of glacial formation or growth.

Yes, you are correct, there is a missing word: ‘temperature’. But this solid error, in my mind, is weighed up by the spectacular name of the bivalve they mention living in this environment: Isorropodon nyeggaensis (sounds more like a dinosaur…). However, the Nyegga area is really a spectacular location, where I worked in 2003 and 2004, doing investigations for Statoil.

Anthony….The title of the article seems a bit misleading, perhaps. Don’t hydrates generally dissociate into their component parts rather than “melt”? So this can include simple diffusion, sublimation, and more exotic solid phase transitions as well as dissociation into supercooled water and methane. Just a thought for clarity’s sake! Thanks

What causes the hydrate to dissociate as the sediment thickness increases? Does the temperature increase with thicker sediment load? Or is there high range of pressure? Anyone have a phase chart at hand?

When dozens of meters of new sediment settle on the seafloor, the solid compounds dissociate at the base of the hydrate stability zone, while new hydrates can form at the upper end of the stability zone.

A good geological read! Not so common these days with the terrible corruption of this once most eloquent of all sciences. I fell in love with geology as a student and was deflected away from the hard sciences by the romance of it.

Geologists are essentially forensic scientists. Detectives. One gathers all the evidence (employing the hard sciences plus biology and mathematics) to untangle an event as much as 4 billion yrs in the past. When you can make predictions from it in examining geology in other parts of the world, and I dare to say extra terrestrial locales as well, then it’s hard to imagine a more gratifying feeling in your professional life.

Earth geological history is so rich. Even pre-life. In the Archean (4b-2.5bybp) earth cooled enough to form solid rock. Komatiites, basaltic volcanics that were hot enough for the lava to melt channels in the the solid silicate crustal rocks are preserved in the Precambrian shields of the continents – part of the ongoing cooling of the young earth. Life in the seas and the evolution that brought us exotic, unimaginably other-worldly eras….

To me the rot set in when we renamed the science “earthsciences” – following the path of the wannabe long-corrupt social sciences who needed to incorporate the word “science” to give a sense of status. Geology didn’t need that. The rationale (apparently) was because we had specialties like geophysics and geochemistry. Heck, I was proficient in both of these geological tools, too, when I graduated and I still can interpret geophysical and geochemical surveys for mining and even petroleum, although admittedly unpracticed in the latter.

I don’t buy this, how come so much vulnerable Methane Hydrate had survived the end of the iceage before the last one, and then iterate back through the iceages to some golden time for the production of Methane Hydrate?

The methane and higher hydrocarbons occurring in the Nyegga area are produced deep down, in a thermogenic way (not only by shallow bacterial means). This is why there is plenty of hydrates in the area and also plenty of fluid-flow features, such as pockmarks and gas hydrate pingoes in this area. It is indeed a spectacular area.

A quick look at several phase diagrams for methane hydrate show no dissociation at higher pressure unless the hydrate is sufficiently buried by sediment to increase the temperature. So it is possible to have a sediment layer that insulates the hydrate and it warms to the dissociation condition, but the layer would need to be hundreds of meters thick. I would like to know the proposed mechanism used in this study.

Methane hydrates form and dissociate all the time as sea-level and water-temperatures shift up and down over glacial cycles. It’s no big deal. Very little of the methane ever reaches the atmosphere. Methane is food, and food does not stay uneaten long either in the sea or in the seabed.

If, hypothetically, the increase in volume (causing rising seas/greater depth) is purely from a temperature rise (expansion) then the mass overlying the seafloor has not increased, therefore the pressure at the floor will not increase.

If, hypothetically, the increase in volume is due to glacial melt, then the rising seas are due to greater mass and the pressure at the floor will rise.

Years ago one of the theories for the end f the last glaciation was that a meteor struck the floor of the Voring Plateau releasing methane causing a warm up due to its GHG capability. There is supposedly a large dimple as evidence of the strike.

It is often overlooked in discussions of glaciation that the earth itself is a heat source. Heat from Earth’s interior to the surface is estimated at 47 terawatts (TW) and comes from two main sources in roughly equal amounts: the radiogenic heat produced by the radioactive decay of isotopes in the mantle and crust, and the primordial heat left over from the formation of the Earth.
Geothermal heat is *constantly* rising through the crust. If it reaches the surface at the bottom of a layer of ice, it will heat the ice until it melts. The temperature of a glacier where it contacts the ground is the melting point of the ice.
Glaciers are dynamic – always melting AND always gathering more snow and ice. It is the difference between the rates of these processes at any given moment that decides whether the NET result is glaciation, stagnation, or de-glaciation.